There are many ways to achieve your goal. Depending on the source of your coordinates, you can fix this in javascript or css. (And I see your using MapBox, perhaps the thing you want to do is also available within that library, but that is out of scope for this question).

Javascript

Lets say your source is a list of coordinates:

var coords = [
[0, 0],
[0, 800],
[400, 400],
[800, 0]
[800, 800]
]

These coordinates are based on a field of size 800x800. Lets call this the baseSize.

CSS

In case your coordinates are static (eg. you want a dot in the left top, center bottom, right bottom etc) you can also just use CSS, no scripts needed. You can think of the coordinates as percentages; given a container of 800x800